Memory impairment has been acknowledged as a core cognitive deficit in schizophrenia, and it is present irrespective of specific features related to the patient or the evolution of the disorder. It is suggested that distinct functional subsystems of memory are differently impaired in these patients, hence the broad range of levels of functioning affected in this specific population. The aim of this study was to assess working memory performance in multiple episode schizophrenia patients. A group of patients diagnosed with schizophrenia and a control group of healthy subjects were comparatively evaluated with 3 neurocognitive tests which require the use of working memory subsystems. Our results indicate significantly poorer performance in the case of patients suffering from schizophrenia, in all three working memory tests - they displayed impaired face recognition abilities and used a significantly higher number of non-list words when asked to repeat a list of words, which may be particularly relevant for their social functioning. The neurobiological and genetic background of the memory impairment in schizophrenia have been acknowledged due to increasing body of evidence, and the current study supports the current data which state that working memory deficits in schizophrenia are consistent, stable and comprehensive. This is particularly relevant for the personal management, and also for the academic, interpersonal and social rehabilitation of schizophrenia patients.
Keywords: schizophrenia, working memory, impairment, cognitive tests
A great number of studies have revealed cognitive deficits in schizophrenia patients, irrespective of the stage of the disorder. Memory dysfunction has been identified through specific tests as a core feature of the cognitive impairment in schizophrenia, and research suggests that it is not correlated with intellectual performance or IQ levels in particular (Zihl et al, 1998, Leeson et al, 2008). Distinct aspects of implicit and explicit memory are differently impaired, according to the memory subtype underlying the specific task involved in the test (Danion et al, 2001, Perry et al, 2001).
Performances of schizophrenia subjects significantly depend on memory type and system employed for the task, and also on the memory task itself (Turetsky et al, 2002).
Working memory is limited in volume and time span, allowing the subject to operate with bits of recent information (Westen, 2006) - for example, retaining the digits of a telephone number, from its reading until the call is made (Twamley et al, 2006), or drawing a figure right after it was seen. It also entails temporary storage and manipulation of information necessary for complex cognitive tasks such as language comprehension, learning, abstract thinking (Twamley et al, 2006), problem-solving related to spatial tasks - spatial working memory (Westen, 2006), generating novel problem solving strategies, understanding the meaning of complex texts, planning oral communications, daily activities or a trip (Zihl et al, 1998). This cluster of functions was conceptualized as ?executive function working memory" (Twamley et al, 2006), and it is suggested that prefrontal areas play a significant role in its functioning (Zihl et al, 1998). Verbal memory is also regarded as a distinctive type of working memory, underlying encoding through language (Ragland et al, 2004, Barch and Csernansky, 2007). Baddeley, who had a significant contribution to the coining of the term working memory in cognitive psychology, emphasizes that working memory has two subsystems: the visuo - spatial sketchpad and the phonological loop. The first one is represented by the working memory for visual and spatial information, and the second one - the short term memory for acoustic or speechbased information. The two aforementioned subsystems are under the control of a central executive system (Baddeley, 1996).
The hippocampus is the most important among the cortical areas contributing to the verbal declarative memory. …